As a protocol for an ad-hoc network formed by node devices performing an intermittent operation, there is a protocol that synchronizes inactive time periods such as sleep time periods with each other between node devices. As such a protocol, Sensor-MAC (S-MAC) has been known.
In addition, as a related technique, a wireless communication system has been known that includes a base station broadcasting a traffic indication message including first bit map information and second bit map information. The first bit map information indicates whether or not traffic exists with respect to a sleep mode ID group obtained by grouping a plurality of sleep mode IDs. The second bit map information indicates whether or not traffic occurs that corresponds to each sleep mode ID belonging to the sleep mode ID group. A terminal is assigned with one of the plural sleep mode IDs, and when having received a traffic indication message, the terminal determines, using the first bit map information, whether or not traffic exists in the sleep mode ID group to which the terminal itself belongs. When traffic exists in the sleep mode ID group to which the terminal itself belongs, the terminal determines, using the second bit map information, whether or not traffic for the terminal itself exists.
As another related technique, a wireless device has been known that is equipped with a processor acquiring a timing from a wireless communication network and monitoring, for the sake of peer-to-peer communication, a frame from another wireless device during a specified time interval determined on the basis of the timing from the communication network. The processor maintains a sleep state between the specified time intervals and wakes up prior to each specified time interval so as to monitor a frame from another wireless device.
As another related technique, a wireless sensor network has been known that is provided with a base station node equipped with a path construction mechanism, a data collection mechanism, and a path reconstruction mechanism. On the basis of the location information of wireless sensor nodes and mutual radio wave intensities, the path construction mechanism constructs a stable path in a tree shape and divides the path into groups. The data collection mechanism performs data collection from each group of the wireless sensor nodes, that is, acquires sensor data from a wireless sensor node serving as a group parent. When the data collection mechanism has failed in the data collection owing to a bad radio wave condition between the wireless sensor nodes, the path reconstruction mechanism does not perform path reconstruction immediately, and when the data collection mechanism has failed in the data collection more than M times, the path reconstruction mechanism performs path reconstruction.
Japanese National Publication of International Patent Application No. 2008-502275, Japanese Laid-open Patent Publication No. 2011-155653, and Japanese Laid-open Patent Publication No. 2007-243794 disclose related techniques.
In a network that synchronizes inactive time periods with each other between node devices, the relay of a packet is completed within an active time period between an inactive time period and a subsequent inactive time period, and hence, a transmission delay is reduced. However, when the network becomes large, the transmission time of a packet increases. Therefore, an inactive time period decreases with an increase in the size of the network.